An object to be authenticated or identified is sometimes provided with a specific marking, which can be part of the object itself or can be coupled to the object. For example, a commonly used marking is a bar code, which includes a linear array of elements that are either printed directly on an object or on labels that are coupled to the object. These elements typically include bars and spaces, with bars of varying widths representing strings of binary ones, and spaces of varying widths representing strings of binary zeros. While bar codes are useful for tracking locations or identities of objects, these markings can be readily reproduced and, thus, have limited effectiveness in terms of preventing counterfeiting.
It is against this background that a need arose to develop the luminescent materials described herein.